Variable output gear pump and motor

ABSTRACT

A gear pump and motor having a plurality of pumps and motors, each of which have at least three gears interengaged with one another, seal members disposed adjacent to the gears, and control means for selectively controlling the movement of the seal members toward or away from the gears of the pump and motors so as to selectively actuate the pumps and motors so as to attain a desired output.

I United States Patent 11 1 1111 3,873,241 Motomura 5] Mar. 25, 1975 VARIABLE OUTPUT GEAR PUMP AND [56] References Cited MOTOR UNITED STATES PATENTS [75] Inventor: Mitsuteru Motomura, Kamakura, 3,063,795 2/ 962 Lauck I 1 9 3 Japan 3,427,985 2/1969 Difford 418/126 3,597,131 8/1971 Schofield et a1. 418/126 1 1 g ee Kabushlkl a s a Komats 3,695,783 10/1972 Soyland et a1. 417/286 Seisakusho, Tokyo, Japan 3,709,639 1/1973 Suda et a1. 417/505 [22] Flled: July 1973 Primary Examiner-John J. Vrablik [21] Appl. No.: 377,964 Attorney, Agent, or Firm-Oblon, Fisher, Spivak,

McClelland & Maier [30] Foreign Application Priority Data 57] ABSTRACT July 10, 1972 Japan 47-68219 July 10 1972 Japan 47-6822O A gear pump and motor. havmg a plurahty of pumps Jul 1972 m an 47 68694 and motors, each of which have at least three gears y p interengaged with one another, seal members disposed [52] U S Cl 417/283 417/286 417/310 adjacent to the gears, and control means for selec- 418/126 418/131 418/196 tively controlling the movement of the seal members [51] Int Cl F04!) 49/00 FOIC [W02 #03: 3/00 toward or away from the gears of the pump and mo- [58] Fie'ld "s' 418/ l25 129 tors so as to selectively actuate the pumps and motors so as to attain a desired output.

20 Claims, 19 Drawing Figures I PMENTEB 3.87am].

' SHEET UBUF 17 PAn-imw SHEET CHUF 17 PMENTED MR 2 5 I975 SHEET UBUF 17 NVN PATENTEU sum 13 or 17 wow ow t mow SHEET 15oF 17 k PE woj H m A. L 1 30 NQV wow .I show m? PATENTEUHARZS W5 sum 17UF 17 wow VARIABLE OUTPUT GEAR PUMP AND MOTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a gear pump and motor, and more particularly to an improved gear pump and motor adapted for efficient operation at low speeds and having means for controlling the position of a sealing member relative to the gears within the pump and motor.

2. Description of the Prior Art Conventional gear pumps and motors are generally of the pressure balance type which tend to improve the pump and motor efficiency by actuating the seal member to a position adjacent to the engaging area of the meshed gears by utilizing the discharge or supply pressure so as to prevent internal oil leakage from the sealing chamber formed by means of the gears and the seal member. The seal member utilized within the conventional gear pumps and motors is thus urged to perform the sealing function in response to the discharge or supply pressure of the oil, and consequently is always actuated in the biased direction. A common occurrence experienced with various construction and industrial machinery employing such gear pumps and motors of the pressure balance type is the reduction in the pumping efficiency and improper responsiveness of the hydraulic components during low speed operation of the drive source and seizure and wear of the seal and rotary members during high speed operation.

Furthermore, when the gear pump and motor is in the idle condition, wherein work is not provided, or the volume discharge of oil which is supplied is more than the required amount, as the pump hydraulic circuit always maintains a hydraulic resistance of approximately l-l5kg/cm such operation results in the consumption of some required power, and yet the discharged hydraulic oil is merely circulating throughout the pump and oil tank. Such operation, however merely consumes power and further increases the temperature of the oil with the result that such is not desirable for cithcr the pump or the conduits and actuators within the hydraulic circuit for the increase in the oil temperature reduces the viscosity of the oil, and accordingly, such results in the decrease of the sealing effect of the seal members whereupon an increase in the internal oil leakage will occur which in turn causes oil leakage within the circuit conduits and actuators. In order to.

prevent such disadvantages, it is usually necessary to enlarge the conduits and valves so as to reduce the fluid resistance, however, in order to enlarge the valves and conduits, it ssometimes becomes difficult to mount the same upon a vehicle, and in addition, it usually is not economical to do so.

The conventional gear pumps and motors have been generally used heretofore for transmission pumps, brake pumps, steering pumps, actuator pumps, or the like, but with respect to the operation of transmission pumps, brake pumps, and steering pumps, such pumps are required to perform their functions even during the idling operation of the engine which is used as a drive source of the pump. However, as the volume efficiency of the pumps of this type isgenerally reduced when the rotational speed is decreased, and particularly when the oil temperature is high, the volume efficiency may become 50 percent or less, the idling speed of the engine of the construction machinery being approximately 500 600 rpm. Under such conditions, even simple operations are difficult to perform often or coordinate,

In order to counteract such disadvantages, the speed of the drive source must be increased, or a pump having a larger volume discharge must be preselected, However, such requirements can be inconvenient, and the power loss noted heretofore is not resolved. If a pump having a sufficient capacity for supplying enough oil even during low speed operation of the engine is adopted, it has been noted that excessive torque is produced, and excessive volume discharge must be released through means of a relief valve during high speed operation thereof which of course is not preferable.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved gear pump and motor which may efficiently control the hydraulic fluid volume dis charge in response to the load.

Another object of the present invention is to provide an improved gear pump and motor which has a plurality of pumps and motors capable of being selectivelydriven or stopped in response to the load.

Still another object of the present invention is to provide an improved gear pump and motor which may prevent a substantial temperature increase of the hydraulic fluid and which may restrict the power loss of the prime mover for the gear pump and motor by controlling the discharge pressure and volume of the fluid, the rotation speed of the pump and motor, and the external force applied thereto.

Yet another object of the present invention is to provide an improved gear pump and motor which may sufficiently compensate for the conventional reduction in volume efficiency during low speed operation of the drive source for the pump and motor, and the wear of the seal member and other pump components due to long periods of usage during high speed operation.

A further object of the present invention is to provide an improved gear pump and motor in which the degree of sealing between the gears and the seal member may be selected at an optimum value so as to prevent the wear and seizure of the seal member by the rotary com ponents during high speed operation.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features, and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several views, and wherein:

FIG. 1 is a graph showing the relationship between the volume efficiency and pump drive speed of a conventional gear pump and motor;

FIG. 2 is a graph showing the relationship between the fluid leakage and seal gap of a conventional gear pump and motor;

FIG. 3 is a schematic view, partly in section, of one embodiment ofa gear pump and motor constructed according to the present invention and showing its cooperative parts;

FIG. 4 is a view similar to that of FIG. 3, showing however the gear pump and motor under high speed operative conditions;

FIG. 5 is another embodiment of a control valve which may be utilized within the gear pump and motor shown in FIGS. 3 and 4;

FIG. 6 is a view similar to that of FIG. 3 showing however another embodiment of a gear pump and motor constructed according to the present invention and showing it cooperative parts;

FIG. 7 is a view similar to that of FIG. 6, showing however the gear pump and motor under high speed operative conditions;

FIG. 8 is a view similar to that of FIG. 3 showing however still another embodiment of a gear pump and motor constructed according to the present invention and showing its cooperative parts;

FIG. 9 is a partial, cross-sectional view of the gear pump and motor of FIG. 8 taken along the line IXIX in FIG. 8;

FIG. 10 is a view similar to that of FIG. 8, showing however the gear pump and motor under high speed operative conditions;

FIG. 11 is a view similar to that of FIG. 3 showing however yet another embodiment of a gear pump and motor constructed according to the present invention and showing its cooperative parts;

FIGS. 12 and 13 are views similar to that of FIG. 11, showing however the gear pump and motor under various operative conditions whereby the output torque and speed may be varied;

FIG. 14 is a schematic view of a further embodiment ofa gear pump and motor constructed according to the present invention and showing its cooperative parts;

FIG. 15 is a view similar to that of FIG. 14, showing however the gear pump and motor under high speed operative conditions;

FIG. 16 is a view similar to that of FIG. 14 showing however a still further embodiment of a gear pump and motor constructed according to the present invention and showing its cooperative parts, the gear pump and motor being under high speed operative conditions;

FIG. 17 is a view similar to that of FIG. 16 showing however the gear pump and motor under low speed operative conditions;

FIG. 18 is a view similar to that of FIG. 14 showing however a still further embodiment of a gear pump and motor constructed according to the present invention and showing its cooperative parts, the gear pump and motor being under high speed operative conditions; and

FIG. 19 is a view similar to that of FIG. 18 showing however the gear pump and motor under low speed operative conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to better understand the gear pump and motor of the present invention, the characteristics of a conventional gear pump and motor will first be described with particular reference to FIGS. 1 and 2, which are performance graphs respectively illustrating the relationship between the pump drive speed and the volume efficiency, and the relationship between the seal gap and the amount of fluid leakage.

Conventional gear pumps and motors are usually of the pressure balance type which have a seal member within the vicinity of the area in which the gears engage, and which is urged toward the gears by utilization of the discharge or supply pressure so as to prevent oil from leaking from the sealing chamber formed by means of the seal member and the gears. When such conventional gear pumps and motors are utilized particularly in conjunction with various construction machinery, the efficiency of such gear pumps and motors is reduced during low speed operation of the engine with the result that the response ofthe various hydrau' lic components and devices is also reduced. In addition, when the engine is operated at high speeds, the seal member readily becomes seized or worn by the rotary members.

As noted heretofore, the conventional gear pumps and motors of the pressure balance type operate such that when the drive speed is decreased, the volume efficiency is also decreased as shown in FIG. 1, and when the temperature of the hydraulic oil increases, the volume efficiency is reduced still further with the result that the volume efficiency is sometimes reduced to a value approximately 50 percent. Construction machinery such as for example, tractors and bulldozers, ordinarily utilize idling engine speeds of approximately 500 600 r.p.m., and in order to compensate for the reduced responsiveness of the hydraulic components and devices, such as for example, the transmission pump, brake pump, steering pump, or workingpump, during low speed operation of the engine, the idling speed of the engine is ordinarily raised or the output capacity of the hydraulic devices is ordinarily increased, but these techniques merely serve to increase the power loss.

Furthermore, the amount of internal hydraulic leakage from the seal gap between the seal member and the gears is generally proportional to the cube of the gap, and has the tendency shown in FIG. 2 wherein curve a illustrates the amount of leakage from the gap between the end portions of the gear teeth and the seal block, curve b represents the amount of leakage from the gap between the side surfaces of the gears and the sides of the seal member, and curve c illustrates the amount of leakage fromthe gap between the seal block and the sides of the seal member.

The gear pump and motor of the present invention seeks to control the actuation of the seal member by. means of the discharge pressure, thedischarge flow rate, the rotational speed of the pump, or by an external force, so as to effectively control the pump discharge and pressure whereby the temperature of the hydraulic oil will be prevented from appreciably rising, and the volume efficiency will be substantially improved, and wear of the pump components will be reduced.

Reference is now made to FIG. 3 in which there is shown a first embodiment of the gear pump and motor constructed according to the present invention as including a housing 1 in which a drive gear 3, driven by a prime mover, not shown, and driven gears 4 and 5 intermeshed with the drive gear 3, are respectively, rotatably supported. Laterally extending intake ports 7 and 8, and exhaust ports 10 and 11, are provided within the walls of the housing 1, and a seal block B1 is disposed within the vicinity of the engaging area S1 between the drive gear 3 and the driven gear 4 so as to form with housing 1 and gears 3 and 4, a first pump and motor, generally indicated by the reference character Pl. A seal block B2 is likewise provided within the vicinity of 

1. A gear pump comprising: a fluid reservoir; a hydraulic actuator fluidically connected to said reservoir; a plurality of pump means being simultaneously driven by a prime mover and interposed between said fluid reservoir and said actuator; a drive gear and at least two driven gears intermeshed with said drive gear mounted within each of said pump means; seal members disposed within the vicinity of the engaging areas between said drive gear and said driven gears; a plurality of control valve means each of which has two ports, and a spool slidably disposed therein so as to be movable between a first position at which said ports are disconnected from each other and a second position at which said ports are in communication with each other; means for introducing the discharge pressure of a previously actuated pump means to the seal members of a successive pump means; means for conducting the resulting pressure to said control valve means; and spring means disposed so as to urge said spools against the hydraulic pressure supplied to said spools for controlling the force applied to said seal members so as to permit said seal members to move toward or away from said gears of said pump means.
 2. A gear pump as set forth in claim 1, wherein all of said seal members of said pump means are controlled by external hydraulic pressure means for moving all of said seal members toward and away from said gears within said pump means.
 3. A gear pump as set forth in claim 1, wherein said gear pump further includes means for detecting the rotational speed of said pump means for controlling the movement of said seal members toward and away from said gears within said pump means.
 4. A gear pump as set forth in claim 1, wherein said plurality of pump means further include seal side plates disposed adjacent to said seal members and slidably and sealingly inserted within grooves formed upon the interior surface of the gear pump housing, said seal side plates being of such width relative to a line connecting the axes of said engaged gears so to completely cover the arcuate sealing portions of said engaged gears for sealing the engaging areas between said drive gear and said driven gears together with said seal members.
 5. A gear pump as set forth in claim 1 wherein said other seal members are always controlled in response to the discharge pressure of previously actuated pump means for moving said other seal members toward and away from said gears within successively actuated pump means.
 6. A gear pump as set forth in claim 5, further comprising: a manifold valve hydraulically connected to all of said pump means at one side thereof and to said actuator at the other side thereof; wherein said control valve means are respectively associated with said successively actuated pump means; and said spring means of said control valve means each having a predetermined spring constant; Whereby said control valve means control the movement of said seal members toward and away from said gears within said pump means in accordance with the pressure differential between the pilot pressure supplied from the output of said manifold valve to said control valve means at one side thereof and said tension of said spring means disposed upon the other side thereof.
 7. A gear pump as set forth in claim 5: wherein said pump means further include respectively, a throttle member disposed within the output hydraulic circuit thereof; said control valve means are respectively associated with said successively actuated pump means; and said spring means of said control valve means each have a predetermined spring constant; whereby said control valve means control the movement of said seal members toward and away from said gears within said pump means in accordance with the pressure differential between the pilot pressure supplied from the output of said pump means to one side of said control means and the pilot pressure supplied from the throttle of said pump means to the other side of said control means.
 8. A gear pump and motor comprising: a fluid reservoir; a pump fluidically connected with said reservoir; an actuator fluidically connected with said reservoir and said pump; a plurality of motor means hydraulically connected to said fluid reservoir and to said pump; a drive gear and at least two driven gears intermeshed with said drive gear and rotatably mounted within each of said motor means; seal members disposed within the vicinity of the engaging area between said drive gear and said driven gears; said motor means being simultaneously connected to said actuator; a plurality of control valve means, each of which respectively have two ports and a spool slidably disposed therein so as to be movable between a first position at which said ports are disconnected from each other and a second position at which said ports are in communication with each other; means for introducing the discharge pressure of a previously actuated motor means to the seal members of a successive motor means; means for conducting the resulting pressure to said control valve means; and spring means disposed so as to urge said spools against the hydraulic pressure supplied to said spools for controlling the force applied to said seal members so as to permit said seal members to move toward or away from said gears of said motor means.
 9. A gear pump and motor as set forth in claim 8 wherein all of said seal members of said motor means are controlled by external hydraulic pressure means for moving all of said seal members toward and away from said gears within said motor means.
 10. A gear pump and motor according to claim 8: wherein said gear pump and motor further includes means for detecting the rotational speed of said motor means for controlling the movement of said seal members toward and away from said gears within said motor means.
 11. A gear pump and motor according to claim 8, wherein said plurality of motor means further include seal side plates disposed adjacent to said seal members and slidably and sealingly inserted within grooves formed upon the interior surface of the gear pump and motor housing, said seal side plates being of such width relative to a line connecting the axes of said engaged gears as to completely cover the arcuate sealing portions of said engaged gears for sealing the engaging areas between said engaged gears tOgether with said seal members.
 12. A gear pump and motor as set forth in claim 8, wherein said other seal members are always controlled in response to the supply pressure to previously actuated motor means for moving said other seal members toward and away from said gears with successively actuated motor means.
 13. A gear pump and motor as set forth in claim 12 further comprising: a manifold valve hydraulically connected to all of said motor means at one side thereof and to said actuator at the other side thereof; wherein said control valve means are respectively associated with said successively actuated motor means; and said spring means of said control valve means each have a predetermined spring constant, whereby said control valve means control the movement of said seal members toward and away from said gears within said motor means in accordance with the pressure differential between the pilot pressure supplied from the output of said manifold valve to said control valve means at one side thereof and said tension of said spring means disposed upon the other side thereof.
 14. A gear pump and motor as set forth in claim 12: wherein said motor means further include respectively, a throttle member disposed within the output hydraulic circuit thereof; said control valve means are respectively associated with said successively actuated motor means; and said spring means of said control valve means each have a predetermined spring constant, whereby said control valve means control the movement of said seal members toward and away from said gears within said motor means in accordance with the pressure differential between the pilot pressure supplied from the output of said motor means to one side of said control means and the pilot pressure supplied from the throttle of said motor means to the other side of said control means.
 15. A gear pump comprising: a housing; a drive gear and at least three driven gears intermeshed with said drive gear and rotatably mounted within said housing; first pump means including said drive gear and one of said driven gears; a first seal member disposed within the vicinity of the engaging area between said drive gear and one of said driven gears; second pump means including said drive gear and a second one of said driven gears; a second seal member disposed within the vicinity of the engaging area between said drive gear and a second one of said driven gears; third pump means including said drive gear and a third one of said driven gears; a third seal member disposed within the vicinity of the engaging area between said drive gear and the third one of said driven gears; first control valve means having a spool slidably disposed therein, and first spring means of predetermined tension for urging said spool to a first position from one end thereof against the hydraulic pressure of the output fluid of said first and second pump means for permitting said second seal member of second pump means to be moved toward said drive gear and said second one of said driven gears in response to the hydraulic pressure of the output fluid of said first pump means, said spool also being movable to a second position at which said hydraulic pressure is exhausted so as to release said second seal member; and second control valve means having a spool slidably disposed therein, and second spring means of predetermined tension for urging said spool to a first position from one end thereof against the hydraulic pressure of the output fluid of said first, second, and third pump means for permitting said third seal member of said third pump means to be moved toward said drive gear and said third one of said driven gears in response to the hydraulic pressure of the output fluid of said first and second pump means, said spool also being movable to a second position at which said hydraulic pressure is exhausted so as to release said third seal member.
 16. A gEar pump and motor comprising: a pump; a housing fluidically connected with said pump; a drive gear and at least three driven gears intermeshed with said drive gear and rotatably mounted within said housing; first motor means including said drive gear and one of said driven gears; a first seal member disposed within the vicinity of the engaging area between said drive gear and one of said driven gears; second motor means including said drive gear and a second one of said driven gears; a second seal member disposed within the vicinity of the engaging area between said drive gear and said second one of said driven gears; third motor means including said drive gear and a third one of said driven gears; a third seal member disposed within the vicinity of the engaging area between said drive gear and the third one of said driven gears; first control valve means having a spool slidably disposed therein, and a first spring means of predetermined tension for urging said spool to a first position from one end thereof against the hydraulic pressure of the output fluid of said first and second motor means for permitting said second seal member of said second motor means to be moved toward said drive gear and said second one of said driven gears in response to the hydraulic pressure of the output fluid of said first motor means, said spool also being movable to a second position at which said hydraulic pressure is exhausted so as to release said second seal member; and second control valve means having a spool slidaby disposed therein, and second spring means of predetermined tension for urging said spool to a first position from one end thereof against the hydraulic pressure of the output fluid of said first, second, and third motor means for permitting said third seal member of said third motor means to be moved toward said drive gear and the said third one of said driven gears in response to the hydraulic pressure of the output fluid of said first and second motor means, said spool also being movable to a second position at which said hydraulic pressure is exhausted so as to release said third seal member.
 17. A gear pump comprising: a prime mover; a housing; a drive gear driven by said prime mover and at least three driven gears intermeshed with said drive gear and rotatably mounted within said housing; first pump means including said drive gear and one of said driven gears; a first seal block disposed within the vicinity of the engaging area between said drive gear and one of said driven gears; a first set of side balance chambers formed upon the outer surface of said first seal block which are in communication with the area formed between the teeth of said drive gear and said one of said driven gears and with each other; a central balance chamber also formed upon the outer surface of said first seal block which is in communication with and annularly surrounds a first exhaust passage formed with said first seal block; second pump means including said drive gear and a second one of said driven gears; a second seal block disposed within the vicinity of the engaging area between said drive gear and said second one of said driven gears; a second set of side balance chambers formed upon the outer surface of said second seal block which are in communication with each other; a central balance chamber also formed upon the outer surface of said second seal block which is in communication with and annularly surrounds a second exhaust passage formed within said second seal block; a first set of passage means within said housing for providing communication between said second set of side balance chambers and the area exterior of said housing; third pump means including said drive gear and a third one of said driven gears; a third seal block disposed within the vicinity of the engaging area between said drive gear and said third one of said driven gears; a third set of sIde balance chambers formed upon the outer surface of said third seal block which are in communication with each other; a central balance chamber also formed upon the outer surface of said third seal block which is in communication with and annularly surrounds a third exhaust passage formed within said third seal block; a second set of passage means within said housing for providing communication between said third set of side balance chambers and the area exterior of said housing; first control valve means having two ports which are in communication with each other when said first control valve means is affected by a first set of hydraulic conditions and which are shut off from each other when said first control valve means is affected by a second set of hydraulic conditions; a first spool slidably disposed within said first control valve means; first spring means so disposed as to urge said first spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three pumps and for permitting said spool to move to a second position and said second seal block to be released from the biased position toward said drive gear and said second one of said driven gears when said hydraulic pressure of said exhaust ports of said pumps exceeds a predetermined value; second control valve means having two ports which are in communication with each other when said second control valve means is affected by a third set of hydraulic conditions and which are shut off from each other when said second control valve means is affected by a fourth set of hydraulic conditions; a second spool slidably disposed within said second control valve means; and second spring means so disposed as to urge said second spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three pumps and for permitting said spool to move to a second position and said third seal block to be released from the biased position toward said drive gear and said third one of said driven gears when said hydraulic pressure of said exhaust ports of said pumps exceeds a predetermined value.
 18. A gear pump and motor comprising: a pump; a housing fluidically connected with said pump; a drive gear and at least three driven gears intermeshed therewith and rotatably mounted within said housing; first motor means including said drive gear and one of said driven gears; a first seal block disposed within the vicinity of the engaging area between said drive gear and said one of said driven gears; a first set of side balance chambers formed upon the outer surface of said first seal block which are in communication with the area formed between the teeth of said driven gear and said one of said driven gears and with each other; a central balance chamber also formed upon the outer surface of said first seal block which is in communication with and annularly surrounds a first exhaust passage formed within said first seal block; second motor means including said drive gear and a second one of said driven gears; a second seal block disposed within the vicinity of the engaging area between said drive gear and said second one of said driven gears; a second set of side balance chambers formed upon the outer surface of said second seal block which are in communication with each other; a central balance chamber also formed upon the outer surface of said second seal block which is in communication with and annularly surrounds a second exhaust passage formed within said second seal block; a first set of passage means within said housing for providing communication between said second set of side balance chambers and the area exterior of said housing; third motor means including said drive gear and a third one of said driven gears; a third seal block disposed within the vicinity of the engaging area between said drive gear and said third one of said driven gears; a third set of siDe balance chambers formed upon the outer surface of said third seal block which are in communication with each other; a central balance chamber also formed upon the outer surface of said third seal block which is in communication with and annularly surrounds a third exhaust passage formed within said third seal block; a second set of passage means within said housing for providing communication between said third set of side balance chambers and the area exterior of said housing; first control valve means having two ports which are in communication with each other when said first control valve means is affected by a first set of hydraulic conditions and which are shut off from each other when said first control valve means is affected by a second set of hydraulic conditions; a first spool slidably disposed within said first control valve means; first spring means so disposed as to urge said first spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three motors and for permitting said spool to be moved to a second position and said second seal block to be released from the biased position toward said drive gear and said second one of said driven gears when said hydraulic pressure of said exhaust ports of said motors exceeds a predetermined value; second control valve means having two ports which are in communication with each other when said second control valve means is affected by a third set of hydraulic conditions and which are shut off from each other when said second control valve means is affected by a fourth set of hydraulic conditions; a second spool slidably disposed within said second control valve means; and second spring means so disposed as to urge said second spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three motors and for permitting said spool to be moved to a second position and said third seal block to be released from the biased position toward said drive gear and said third driven gears when said hydraulic pressure of said exhaust ports of said motors exceeds a predetermined value.
 19. A gear pump comprising: a housing; a drive gear and at least three driven gears intermeshed with said drive gear and rotatably mounted within said housing; first pump means including said drive gear and one of said driven gears; a first seal block disposed within the vicinity of the engaging area between said drive gear and said one of said driven gears; a first seal side plate disposed adjacent to said first seal block and slidably and sealingly inserted within a first groove formed upon the interior surface of said housing; a first recess formed upon the outer surface of said first seal side plate; a first O-ring disposed within said first recess so as to be in contact with the surfaces of said first groove thereby forming a first pressure chamber which is in fluidic communication with said engaging area between said drive gear and said one of said driven gears; second pump means including said drive gear and a second one of said driven gears; a second seal block disposed within the vicinity of the engaging area between said drive gear and said second one of said driven gears; a second seal side plate disposed adjacent to said second seal block and slidably and sealingly inserted within a second groove formed upon the interior surface of said housing; a second recess formed upon the outer surface of said second seal side plate; a second O-ring disposed within said recess so as to be in contact with the surfaces of said second groove thereby forming a second pressure chamber which is in fluidic communication with said engaging area between said drive gear and said second one of said driven gears; third pump means including said drive gear and a third one of said driven gears; a third seal block disposed within the vicinity of the engaging area between said drive Gear and said third one of said driven gears; a third seal side plate disposed adjacent to said third seal block and slidably and sealingly inserted within a third groove formed upon the interior surface of said housing; a third recess formed upon the outer surface of said third seal side plate; a third O-ring disposed within said third recess so as to be in contact with the surfaces of said third groove thereby forming a third pressure chamber which is in fluidic communication with said engaging area between said drive gear and said third one of said driven gears; first control valve means having two ports which are in communication with each other when said first control valve means is affected by a first set of hydraulic conditions and which are shut off from each other when said first control valve means is affected by a second set of hydraulic conditions; a first spool slidably disposed within said first control valve means; first spring means so disposed as to urge said first spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three pumps and for permitting said spool to be moved to a second position and second seal side plate to be released from the biased position toward said drive gear and said second one of said driven gears when the hydraulic pressure of said exhaust ports of said pumps exceeds a predetermined value; second control valve means having two ports which are in communication with each other when said second control valve means is affected by a third set of hydraulic conditions and which are shut off from each other when said second control valve means is affected by a fourth set of hydraulic conditions; a second spool slidably disposed within said second control valve means; and second spring means so disposed as to urge said second spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three pumps and for permitting said spool to be moved to a second position and said third seal side plate to be released from the biased position toward said drive gear and said third one of said driven gears when said hydraulic pressure of said exhaust ports of said pumps exceeds a predetermined value.
 20. A gear pump and motor comprising: a pump; a housing fluidically connected with said pump; a drive gear and at least three driven gears intermeshed with said drive gear and rotatably mounted within said housing; first motor means including said drive gear and one of said driven gears; a first seal block disposed within the vicinity of the engaging area between said drive gear and said one of said driven gears; a first seal side plate disposed adjacent to said first seal block and slidably and sealingly inserted within a first groove formed upon the interior surface of said housing; a first recess formed upon the outer surface of said first seal side plate; a first O-ring disposed within said first recess so as to be in contact with the surfaces of said first groove thereby forming a first pressure chamber which is in fluidic communication with said engaging area between said drive gear and said one of said driven gears; second motor means including said drive gear and a second one of said driven gears; a second seal block disposed within the vicinity of the engaging area between said drive gear and a second one of said driven gears; a second seal side plate disposed adjacent to said second seal block and slidably and sealingly inserted within a second groove formed upon the interior surface of said housing; a second recess formed upon the outer surface of said second seal side plate; a second O-ring disposed within said second recess so as to be in contact with the surfaces of said second groove thereby forming a second pressure chamber which is in communication with said engaging area between said drive gear and said second one of said driven gears; third motor means including said drive gear and a third one of said driven gears; a third seal block disposed within the vicinity of the engaging area between said drive gear and said third one of said driven gears; a third seal side plate disposed adjacent to said third seal block and slidably and sealingly inserted within a third groove formed upon the interior surface of said housing; a third recess formed upon the outer surface of said third seal side plate; a third O-ring disposed within said third recess so as to be in contact with the surfaces of said third groove thereby forming a third pressure chamber which is in fluidic communication with said engaging area between said drive gear and said third one of said driven gears; first control valve means having two ports which are in communication with each other when said first control valve means is affected by a first set of hydraulic conditions and which are shut off from each other when said first control valve means is affected by a second set of hydraulic conditions; a first spool slidably disposed within said first control valve means; first spring means so disposed so as to urge said first spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three motors and for permitting said spool to be moved to a second position and said second seal side plate to be released from the biased toward said drive gear and said second one of said driven gears when the hydraulic pressure of said exhaust ports of said motors exceeds a predetermined value; second control valve means having two ports which are in communication with each other when said second control valve means is affected by a third set of hydraulic conditions and which are shut off from each other when said second control valve means is affected by a fourth set of hydraulic conditions; a second spool slidably disposed within said second control valve means; and second spring means so disposed as to urge said second spool to a first position against the hydraulic pressure supplied from the exhaust ports of said three motors and for permitting said spool to be moved to a second position and said third seal side plate to be released from the biased position toward said drive gear and said third one of said driven gears when said hydraulic pressure of said exhaust ports of said motors exceeds a predetermined value. 